Electrical system of distribution.



J. L. WOODBRIDGE.

ELECTRICAL SYSTEM OF DISTRIBUTION. APPLICATION FILED JUNE 16, 1911.

1,014,355, Patented Jan.9, 1912.

Jose oh Lesfer l Vaoa rldje roman mm WOODBBIDGI, OI PENNSYLVANIA.

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morn-loan 1,014,355. 1 Specific of 1am s Patented J an. 9, 1912.

Application fled June 16, 1911. and In. 688,609. To all whomit may concern: current when electromotive force is a plied Be it known that I, Josarn Lae'ran Woonnniocn, a citizen of the United States, and a resident of Philadelphia, in the count of 5 Philadelphia, State of Pennsylvania, ave

invented certain ments in Electrical Systems of Distribution, of which the following is a specification.

My invention relates to systems in which a dy ployed to furnish electric current at substantially constant potential to a consumption circuit, andv the invention comprises means for controlling the field current of the dynamo to maintain its potential substantially constant with variations of speed. To accom lish this result I provide a combination of circuits connected in the form of a Wheatstone bridge, this bridge being connected bezoftween the opposite conductors of the consumption circuit,.while the field winding is connected across opposite junction points of the bridge. The control of the current in the field of the dynamo is obtairfed b reason of the special characteristics of t e circuits "constituting the several branches of the bridge.

My invention will be clearly understood by reference to the following description 80 taken in connection with the accompanying drawings, in which- Figure 1 is a diagrammatic representation of a system involving features of the invention, and Fig. 2 is a modification of the sys- 85 tem shown in Fig. 1.

Referring to Fig. 1 A is a dynamo connected to the consumption circuit 1-2 which supplies the translating devices L. The dynamo A may be driven by any suitable means at variable speed, as, for example, from the axle of a moving vehicle, such as a railway car, or by the engine of. an automobile. F is the fild winding of the dynamo which is connected across the opposite junction points 3 and 4 of a Wheatstone bridge, the other two junction points 5 and 6 of this bridge being connected to the consumption circuit 1-2. The bridge comprises four branches, in two of which are shown sources of counter electromotive force C and C. These may be counter-electromotive force cells, constructed in .the well known manner by immersing sheets of similar metal, such as lead or platinum in an electrolyte, for example dilute sulfuric acid. Suchcells oppose the flow of new and useful Improveamo driven at variable speed is em to their terminals u to a certain va no of this electromotive orce, but beyond this value current will pass freely throu h the cells. These cells have no capacity or the storage of electrical energy and when the electromotive force at their terminals is reduced below the critical point they cannot discharge. These cells should be so designed that their critical voltage, that' is the aggregate of the critical voltages of all the cells connected in series in each branch, should be equal to one-half of the voltage desired across the-circuit 1-2. In the other two opposite branches of the Wheatstone bridge are shown resistances I and I having a high temperature 'co-eflicient, such as iron wire. These resistances are well known in the art and -for this particular use should be so designed as to have the well known constant current characteristic at one-half the voltage desired across the circuit 1-2. Under these conditions slight variations of voltage above or below this value will not cause any appreciable change of current through these resistances.

The operation oi the apparatus above described will then be, as follows: When the speed of the dynamo A is too low to maintain full volt-age across the circuit 1-2, current will pass from the point 5 of the Wheatstone bridge through resistance 1'. to the point 3, thence through the field winding F to the point 4, and thence through resistance 1 to the point 6 in conductor 2. No appreciable current will flow 'through'the cells C and C since the potential across these cells has not reached the critical value." As the speed of the dynamo increases, the potential across the points 5 and 6 will 1ncrease, producing at first an increase of current through the field F. The -potential across the circuit 1-2 will thus rise rapidly due to the increase of speed and the increase of field excitation until this potential nearly reaches the desired limiting value for which the apparatus has been designed. At this point the potential difierence between point 3 and point- 4 of the Wheatstone bridge will be reduced to a small amount just suflicient to produce the this speed of the dynamo A. The entire current to be carried by the resistances I and I will be passing through the' field F, and this field should be so designed that the field excitation required at Qdifierence of potential across its terminals -When carrying this current will be comparatively small, for example, 5% of the total potential across the circuit 12, the potential of the point 3 being positive with respect to point 4. New assuming that there is a further increase of speed of dynamo A, no greater flow of. current can take place through the field Finn/the reason that the iron wire resistances I and I have reached I their critical condition and maintain their current substantially constant regardless of the impressed voltage. As soon, however, as the potential across the cells 0 and (1 reaches the critical value, a part of the current transmitted through-I and I will flow through these cells thushreducing the amount of current inithe field winding F.

- IAs the potential across the circuit 12 apthis value,

preaches the desired limiting value with increase of speed of dynamo A, the current in the field winding F' Will gradually be reduced.- The potential across the circuit 1 .-2 can never quite, reach the limiting value,

that is, a .valueequal to the sum of the electation- It will beseen, therefore, that the namo A willcontinuallyin combination with resistances of high tem- I ances I and I to pass through the field at a potentlal below the critical value across the circuit 1-2, whereas with resistances inperature co-efiicient in the other two ranches is believed to be new, and constitutes a substantial improvement, since these counter electromotive force cells cause all of the current passing through the resiststead of counter electromotive force cells in these two branches, a part of the'current carried by the resistances I and I will be diverted, and only a part will be transmitted through :the field'F. The introduction of these counter electromotive force cells will, therefore, provide closer voltage regulation, and permit the use of a smaller field winding on the dynamo.-

In Fig. 2 'I'have shown a modification of the described in connection with Fig. 1. Fig. 2 the dynamo is of the well known Rosenberg type'described in United States Patent No. 954,468.. The field windings F and E which provide the primary opposite branches of the bridge note-see excitation at this machine are connected across the Wheatstone bridge just as described in connection with Fig. 1. This Wheatstone bridge is also modified by the addition of resistances R and R in parallel with the counter electromotive force cells C and C respectively. These resistances may be useful to permit the iron wire resistances 1 and I to be designed of comparatively large current carrying capacity sothat they' Havin described my invention what I claim an desire to secure by Letters Patent 1s- 1. In combination, a consumption circuit, a variable speed dynamo connected thereto, a Wheatstone bridge whereof two opposite branches contain counter electromotive force cells, while the *other two'opposite branches contain resistances of high temperature co eflicient, connections from two opposite junction points of the bridge to the consumption circuit and a field winding for the dynamo connected to the other two opposite junction points. I

2. In combination, a consumption circult, a variable speed dynamo connected thereto, .two branch circuits connected in parallel 'across the consumption circuit, whereof one contains a source of counter electromotive force and a high temperature co-eflicient resistance in series, and a field winding for the dynamo connected at one end to a point in the branch circuit between the counter electromotive force cell and the said resistance, and at the other end to an intermediate point in the other branch circuit.

3. The combination of a variable speed dynamo-electric machine having a field winding, with a circuit connected across the -machine terminals containing a counter electromotive force cell and a resistance of high temperature co-eificient, and connection from the field winding to a point in said circuit between the cell and the'resistance.

4. In a system of electrical d1str1but1on comprising a consumption circuit'and its source, the combination of a Wheatstone bridge connected across the consumption circuit and containing respectively counter electromotive force cells and high temperature' co-efiicient resistances in alternate branches, and a field winding for controlling the voltage of the source connected across opposite junction points of the bridge, substantially as described.

5. In a system of electrical distribution comprising a consumption circuit and its source, the combination of a Wheatstone sistances connected in parallel with the bridge connected across the consumption counter electromotive force cells. 0 circuit and containing respectively counter In testimony whereof I havesigned my electromotive force cells and high temperaname.

ture co-eflicient res stances in alternate JOSEPH LESTER WOODBRIDGE. branches, a field winding for controlling the Witnesses: voltage of the source connected across oppo- J. H. TRACY,

site junction points of the bridge; and re- F. G. BEETEM- 

